1. Field of the Invention
The present invention relates generally to a percutaneous catheter for the introduction and withdrawal of fluids from the vascular system of a patient and, more particularly, to a catheter assembly that employs a multi-diameter catheter housing, a proximal end cap for the housing having a central bore therein, and a dilator for passage through the catheter housing and the cap.
2. Description of the Related Art
Under various circumstances in the treatment of a patient experiencing cardiac problems, it is desired to cannulate the patient's vasculature for either blood perfusion or other treatment, such as the insertion of a catheter, a cannulae or an IABP. In a surgical environment, the surgeon typically exposes the blood vessel through a cut-down process. To cannulate the blood vessel, a small slit is made in the vessel wall of a clamped vessel to permit insertion of either an arterial perfusion catheter or a therapeutic catheter for the application of, for example, an IABP. With a perfusion catheter, often an atraumatic tip dilator is positioned concentrically within the catheter over a guidewire to assist in advancing the catheter to the desired point with minimal trauma to the epithelial layer. The dilator and guidewire are then removed and the catheter left in place for treatment.
In an environment such as a cardiac catheterization laboratory, an interventional clinician is not trained to perform a surgical cut down to penetrate the patient's vasculature. Thus, a percutaneous cannulation is necessary. With a percutaneous cannulation, a very small diameter insertion needle having a hollow lumen therein is used to penetrate the vessel wall. Then a guidewire is inserted through the insertion needle, and the needle removed. Next, an angio-cath, which may be made of polyethylene, is inserted over the guidewire, replacing the needle. Where it is desired only to establish a low flow rate of fluid percutaneously, either for aspiration or infusion, the angio-cath is left in place. The angio-cath may then be connected at its proximal end to a source of fluid or a syringe to inject fluid or to remove blood.
Where it is desired to establish a larger flow of fluid or to apply some level of cardiac treatment to the patient, a guide wire may then be inserted within the lumen of the insertion needle to permit removal of the insertion needle, leaving the guide wire in place. Once the guide wire is positioned where desired, an introducer sheath is inserted over the guide wire and through the vessel wall. In order to dilate the wall opening with minimal trauma to the blood vessel, a stylet (dilator) is placed concentrically within the introducer sheath so that both ride over the guide wire to position the sheath within the vessel wall. The dilator has a very small distal diameter to permit easy penetration through the small opening in the vessel wall. The dilator is tapered with increasing diameter toward the proximal end up to the diameter of the sheath so that the opening in the vessel wall is gradually expanded. Once the sheath is positioned within the vessel wall, the dilator is then removed, leaving the sheath within the wall with the guide wire remaining therethrough. The clinician has now established communication with the blood vessel at the desired diameter. The guide wire is then typically advanced into the patient's vasculature as far as is desired to either establish remote fluid communication with the patient or to a point where treatment with an perfusion catheter or other device is desired. For the passage of large devices or for the passage of a large volume of blood, a large diameter introducer sheath is required. With this sheath/guide wire arrangement, the clinician may exchange any one of a number of catheters without risk of losing that communication, because the sheath remains in place. The clinician threads the catheter over the guide wire to the desired location. Even where treatment is discontinued, the sheath may be left in place temporarily to permit the clinician to apply treatment again without having to reopen the blood vessel wall. Typically, the introducer sheath has a hemostasis valve at its proximal end to control the flow of fluid therethrough.
Once the sheath is in place, a perfusion catheter of a desired size (smaller than the sheath, however) may be inserted over the guide wire and through the sheath. The guide wire may then be removed, if so desired. Where fluid communication with the patient is desired at a location remote from the penetration site, a guiding catheter may first be inserted within the sheath and over the guide wire while it is advanced to the desired point in the patient's vasculature. To serve its function as a guide, the guiding catheter typically has a radiopaque marker at the distal end that may be seen through an x-ray monitor via fluoroscopy technique. The marker typically consists of a metallic ring detectable via fluoroscopy by the x-ray. With such a marker, the clinician may follow the location of the distal end as it advances through the vasculature. If desired, radiopaque contrast fluid may be directed through the guiding catheter and out into the vessel at the distal end to permit viewing of the vasculature through which the guiding catheter is passing. This serves the purpose of showing the general profile of the vessel as the guiding catheter is advanced. Such contrast may expose problems with continuing to proceed in that particular vessel before the guiding catheter has advanced too far.
Once the guiding catheter has been advanced to the desired point, an intravascular device, such as an angioplasty balloon, may be inserted the guiding catheter for vascular treatment. Or, a perfusion catheter may be inserted within the guiding catheter as well, to permit blood flow. In either case, it may be desirable to remove both the guiding catheter and the guide wire to permit treatment to be applied. The introducer sheath may be of the type that remains in place, or it may be of the type that tears away, leaving whatever device is in the sheath to maintain the opening in the vessel wall. Once the sheath is removed, however, that device (i.e., a guiding catheter or other device) provides the only vehicle to maintain the vessel wall opening at that diameter.
The advantage of an introducer sheath is that it permits exchange of catheters over time without losing the benefit of an established vessel wall opening. The disadvantage is that it hampers the use of large diameter catheters, i.e., where it is desired to establish fluid communication with the patient's vasculature at high flow rates. With a large diameter introducer sheath, occlusion of the blood vessel may occur, leading to possible ischemia of the limb served by the blood vessel. For example, if it is desired to establish fluid communication on the order of 1.5 liters per minute or greater through the femoral artery, it would be desirable to use a 12 French (outer diameter) perfusion catheter. To do so, however, would require at least a 12 French (inner diameter) introducer sheath. An even larger sheath would be necessary if it were also desired to have a guiding catheter inserted within the sheath and the perfusion catheter inserted within the guiding catheter. Given the size of the femoral artery, such a large introducer sheath has risks of occluding the femoral artery.
Thus, it would be desirable to establish a large fluid flow connection percutaneously to an artery or vein without the need for an introducer sheath or without a guiding catheter, but yet still provide a way of serving the function normally served by a guiding catheter.